Aromatic polysulfones not only exhibit excellent levels of heat resistance, chemical resistance, and creep resistance and the like, but also display good adhesiveness to materials such as metals, glass and ceramics, and are therefore used as all manner of coating materials. One known example of this type of use is a method for forming a fluororesin coating film on a substrate surface by applying an aromatic polysulfone solution containing the fluororesin to a metal substrate and then conducting a heat treatment.
In order to ensure that the aromatic polysulfone has a level of heat resistance suitable for this type of application, it is important that the molecular weight and the molecular weight distribution of the aromatic polysulfone fall within appropriate ranges, and for example, an aromatic polysulfone having a number average molecular weight (Mn) of 11,000 to 25,000 and a polydispersity (Mw/Mn) of not more than 3.0 is already see Patent Document 1).